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  <section id="cmp0077">
<span id="policy:CMP0077"></span><h1>CMP0077<a class="headerlink" href="#cmp0077" title="Link to this heading">¶</a></h1>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.13.</span></p>
</div>
<p><span class="target" id="index-0-command:option"></span><a class="reference internal" href="../command/option.html#command:option" title="option"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">option()</span></code></a> honors normal variables.</p>
<p>The <span class="target" id="index-1-command:option"></span><a class="reference internal" href="../command/option.html#command:option" title="option"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">option()</span></code></a> command is typically used to create a cache entry
to allow users to set the option.  However, there are cases in which a
normal (non-cached) variable of the same name as the option may be
defined by the project prior to calling the <span class="target" id="index-2-command:option"></span><a class="reference internal" href="../command/option.html#command:option" title="option"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">option()</span></code></a> command.
For example, a project that embeds another project as a subdirectory
may want to hard-code options of the subproject to build the way it needs.</p>
<p>For historical reasons in CMake 3.12 and below the <span class="target" id="index-3-command:option"></span><a class="reference internal" href="../command/option.html#command:option" title="option"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">option()</span></code></a>
command <em>removes</em> a normal (non-cached) variable of the same name when:</p>
<ul class="simple">
<li><p>a cache entry of the specified name does not exist at all, or</p></li>
<li><p>a cache entry of the specified name exists but has not been given
a type (e.g. via <code class="docutils literal notranslate"><span class="pre">-D&lt;name&gt;=ON</span></code> on the command line).</p></li>
</ul>
<p>In both of these cases (typically on the first run in a new build tree),
the <span class="target" id="index-4-command:option"></span><a class="reference internal" href="../command/option.html#command:option" title="option"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">option()</span></code></a> command gives the cache entry type <code class="docutils literal notranslate"><span class="pre">BOOL</span></code> and
removes any normal (non-cached) variable of the same name.  In the
remaining case that the cache entry of the specified name already
exists and has a type (typically on later runs in a build tree), the
<span class="target" id="index-5-command:option"></span><a class="reference internal" href="../command/option.html#command:option" title="option"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">option()</span></code></a> command changes nothing and any normal variable of
the same name remains set.</p>
<p>In CMake 3.13 and above the <span class="target" id="index-6-command:option"></span><a class="reference internal" href="../command/option.html#command:option" title="option"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">option()</span></code></a> command prefers to
do nothing when a normal variable of the given name already exists.
It does not create or update a cache entry or remove the normal variable.
The new behavior is consistent between the first and later runs in a
build tree.  This policy provides compatibility with projects that have
not been updated to expect the new behavior.</p>
<p>When the <span class="target" id="index-7-command:option"></span><a class="reference internal" href="../command/option.html#command:option" title="option"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">option()</span></code></a> command sees a normal variable of the given
name:</p>
<ul class="simple">
<li><p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior for this policy is to proceed even when a normal
variable of the same name exists.  If the cache entry does not already
exist and have a type then it is created and/or given a type and the
normal variable is removed.</p></li>
<li><p>The <code class="docutils literal notranslate"><span class="pre">NEW</span></code> behavior for this policy is to do nothing when a normal
variable of the same name exists.  The normal variable is not removed.
The cache entry is not created or updated and is ignored if it exists.</p></li>
</ul>
<p>See <span class="target" id="index-0-policy:CMP0126"></span><a class="reference internal" href="CMP0126.html#policy:CMP0126" title="CMP0126"><code class="xref cmake cmake-policy docutils literal notranslate"><span class="pre">CMP0126</span></code></a> for a similar policy for the <span class="target" id="index-0-command:set"></span><a class="reference internal" href="../command/set.html#cache" title="set(cache)"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">set(CACHE)</span></code></a>
command, but note that there are some differences in <code class="docutils literal notranslate"><span class="pre">NEW</span></code> behavior
between the two policies.</p>
<p>This policy was introduced in CMake version 3.13.
It may be set by <span class="target" id="index-0-command:cmake_policy"></span><a class="reference internal" href="../command/cmake_policy.html#command:cmake_policy" title="cmake_policy"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_policy()</span></code></a> or <span class="target" id="index-0-command:cmake_minimum_required"></span><a class="reference internal" href="../command/cmake_minimum_required.html#command:cmake_minimum_required" title="cmake_minimum_required"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_minimum_required()</span></code></a>.
If it is not set, CMake warns, and uses <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior.</p>
<p>Use the <span class="target" id="index-0-variable:CMAKE_POLICY_DEFAULT_CMP&lt;NNNN&gt;"></span><a class="reference internal" href="../variable/CMAKE_POLICY_DEFAULT_CMPNNNN.html#variable:CMAKE_POLICY_DEFAULT_CMP&lt;NNNN&gt;" title="CMAKE_POLICY_DEFAULT_CMP&lt;NNNN&gt;"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_POLICY_DEFAULT_CMP0077</span></code></a> variable to set the policy for
a third-party project in a subdirectory without modifying it.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior of a policy is
<span class="target" id="index-0-manual:cmake-policies(7)"></span><a class="reference internal" href="../manual/cmake-policies.7.html#manual:cmake-policies(7)" title="cmake-policies(7)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">deprecated</span> <span class="pre">by</span> <span class="pre">definition</span></code></a>
and may be removed in a future version of CMake.</p>
</div>
</section>


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